REVISIONS TO LOWER CARBONIFEROUS HORTON GROUP STRATIGRAPHY IN NEW BRUNSWICK, CANADA

Historically, Lower Carboniferous strata in the Moncton Subbasin of southeastern New Brunswick have been divided into a basal terrestrial sequence, the Horton Group, and an unconformably overlying terrestrial and marine sequence, the Windsor Group. Published works indicate the Horton Group comprises three conformable formations, the basal Memramcook Formation redbeds, the medial Albert Formation grey lacustrine strata and the upper Weldon Formation coarse and fine redbeds. The Horton formations are unconformably succeeded by coarse redbeds of the Hillsborough Formation, which represents the basal mappable unit of the Windsor Group.

Industry-generated seismic reflection profiles and seven exploration wells drilled in the past two years in the McCully gas field east of Sussex indicate that accepted relationships of upper Horton Group stratigraphy are in error. New mapping in the Sussex area supports the seismic interpretations and drilling data. For example, the upper Horton Group is not a depositionally continuous sequence. The Albert Formation is unconformably overlain by a lenticular body of grey, green and red coarse clastic terrestrial strata that shows remarkable lateral thickness variation. The lithology and stratigraphic relationship of this unit is analogous to the Round Hill Formation, a unit that unconformably overlies pre-Carboniferous basement and the Albert Formation in the eastern Moncton Subbasin. The coarse unit (Round Hill Formation) in the Sussex area is unconformably succeeded by the Weldon Formation. The Weldon comprises several hundred metres of red, fine-grained sandstones and mudstones, and in this regard is similar to the section in the type area near Weldon.

Palynological assemblages from the Albert Formation yield middle Tournaisian ages, and are assignable to miospore zones older than Spelaeotriletes cabotii. Palynological collections from the Round Hill Formation in the Sussex area, and north of Moncton, give uppermost Tournaisian ages, that is upper Spelaeotriletes cabotii zone and younger. The Weldon Formation is nearly exclusively a red oxidized unit, and attempts to date it by microflora have proven futile.